// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/filter/gzip_filter.h"

#include "base/bit_cast.h"
#include "base/logging.h"
#include "net/filter/gzip_header.h"
#include "third_party/zlib/zlib.h"

namespace net {

GZipFilter::GZipFilter(FilterType type)
    : Filter(type)
    , decoding_status_(DECODING_UNINITIALIZED)
    , decoding_mode_(DECODE_MODE_UNKNOWN)
    , gzip_header_status_(GZIP_CHECK_HEADER_IN_PROGRESS)
    , zlib_header_added_(false)
    , gzip_footer_bytes_(0)
    , possible_sdch_pass_through_(false)
{
}

GZipFilter::~GZipFilter()
{
    if (decoding_status_ != DECODING_UNINITIALIZED) {
        inflateEnd(zlib_stream_.get());
    }
}

bool GZipFilter::InitDecoding(Filter::FilterType filter_type)
{
    if (decoding_status_ != DECODING_UNINITIALIZED)
        return false;

    // Initialize zlib control block
    zlib_stream_.reset(new z_stream);
    if (!zlib_stream_.get())
        return false;
    memset(zlib_stream_.get(), 0, sizeof(z_stream));

    // Set decoding mode
    switch (filter_type) {
    case Filter::FILTER_TYPE_DEFLATE: {
        if (inflateInit(zlib_stream_.get()) != Z_OK)
            return false;
        decoding_mode_ = DECODE_MODE_DEFLATE;
        break;
    }
    case Filter::FILTER_TYPE_GZIP_HELPING_SDCH:
        possible_sdch_pass_through_ = true; // Needed to optionally help sdch.
        // Fall through to GZIP case.
    case Filter::FILTER_TYPE_GZIP: {
        gzip_header_.reset(new GZipHeader());
        if (!gzip_header_.get())
            return false;
        if (inflateInit2(zlib_stream_.get(), -MAX_WBITS) != Z_OK)
            return false;
        decoding_mode_ = DECODE_MODE_GZIP;
        break;
    }
    default: {
        return false;
    }
    }

    decoding_status_ = DECODING_IN_PROGRESS;
    return true;
}

Filter::FilterStatus GZipFilter::ReadFilteredData(char* dest_buffer,
    int* dest_len)
{
    if (!dest_buffer || !dest_len || *dest_len <= 0)
        return Filter::FILTER_ERROR;

    if (decoding_status_ == DECODING_DONE) {
        if (GZIP_GET_INVALID_HEADER != gzip_header_status_)
            SkipGZipFooter();
        // Some server might send extra data after the gzip footer. We just copy
        // them out. Mozilla does this too.
        return CopyOut(dest_buffer, dest_len);
    }

    if (decoding_status_ != DECODING_IN_PROGRESS)
        return Filter::FILTER_ERROR;

    Filter::FilterStatus status;

    if (decoding_mode_ == DECODE_MODE_GZIP && gzip_header_status_ == GZIP_CHECK_HEADER_IN_PROGRESS) {
        // With gzip encoding the content is wrapped with a gzip header.
        // We need to parse and verify the header first.
        status = CheckGZipHeader();
        switch (status) {
        case Filter::FILTER_NEED_MORE_DATA: {
            // We have consumed all input data, either getting a complete header or
            // a partial header. Return now to get more data.
            *dest_len = 0;
            // Partial header means it can't be an SDCH header.
            // Reason: SDCH *always* starts with 8 printable characters [a-zA-Z/_].
            // Gzip always starts with two non-printable characters.  Hence even a
            // single character (partial header) means that this can't be an SDCH
            // encoded body masquerading as a GZIP body.
            possible_sdch_pass_through_ = false;
            return status;
        }
        case Filter::FILTER_OK: {
            // The header checking succeeds, and there are more data in the input.
            // We must have got a complete header here.
            DCHECK_EQ(gzip_header_status_, GZIP_GET_COMPLETE_HEADER);
            break;
        }
        case Filter::FILTER_ERROR: {
            if (possible_sdch_pass_through_ && GZIP_GET_INVALID_HEADER == gzip_header_status_) {
                decoding_status_ = DECODING_DONE; // Become a pass through filter.
                return CopyOut(dest_buffer, dest_len);
            }
            decoding_status_ = DECODING_ERROR;
            return status;
        }
        default: {
            status = Filter::FILTER_ERROR; // Unexpected.
            decoding_status_ = DECODING_ERROR;
            return status;
        }
        }
    }

    int dest_orig_size = *dest_len;
    status = DoInflate(dest_buffer, dest_len);

    if (decoding_mode_ == DECODE_MODE_DEFLATE && status == Filter::FILTER_ERROR) {
        // As noted in Mozilla implementation, some servers such as Apache with
        // mod_deflate don't generate zlib headers.
        // See 677409 for instances where this work around is needed.
        // Insert a dummy zlib header and try again.
        if (InsertZlibHeader()) {
            *dest_len = dest_orig_size;
            status = DoInflate(dest_buffer, dest_len);
        }
    }

    if (status == Filter::FILTER_DONE) {
        decoding_status_ = DECODING_DONE;
    } else if (status == Filter::FILTER_ERROR) {
        decoding_status_ = DECODING_ERROR;
    }

    return status;
}

Filter::FilterStatus GZipFilter::CheckGZipHeader()
{
    DCHECK_EQ(gzip_header_status_, GZIP_CHECK_HEADER_IN_PROGRESS);

    // Check input data in pre-filter buffer.
    if (!next_stream_data_ || stream_data_len_ <= 0)
        return Filter::FILTER_ERROR;

    const char* header_end = NULL;
    GZipHeader::Status header_status;
    header_status = gzip_header_->ReadMore(next_stream_data_, stream_data_len_,
        &header_end);

    switch (header_status) {
    case GZipHeader::INCOMPLETE_HEADER: {
        // We read all the data but only got a partial header.
        next_stream_data_ = NULL;
        stream_data_len_ = 0;
        return Filter::FILTER_NEED_MORE_DATA;
    }
    case GZipHeader::COMPLETE_HEADER: {
        // We have a complete header. Check whether there are more data.
        int num_chars_left = static_cast<int>(stream_data_len_ - (header_end - next_stream_data_));
        gzip_header_status_ = GZIP_GET_COMPLETE_HEADER;

        if (num_chars_left > 0) {
            next_stream_data_ = const_cast<char*>(header_end);
            stream_data_len_ = num_chars_left;
            return Filter::FILTER_OK;
        } else {
            next_stream_data_ = NULL;
            stream_data_len_ = 0;
            return Filter::FILTER_NEED_MORE_DATA;
        }
    }
    case GZipHeader::INVALID_HEADER: {
        gzip_header_status_ = GZIP_GET_INVALID_HEADER;
        return Filter::FILTER_ERROR;
    }
    default: {
        break;
    }
    }

    return Filter::FILTER_ERROR;
}

Filter::FilterStatus GZipFilter::DoInflate(char* dest_buffer, int* dest_len)
{
    // Make sure we have both valid input data and output buffer.
    if (!dest_buffer || !dest_len || *dest_len <= 0) // output
        return Filter::FILTER_ERROR;

    if (!next_stream_data_ || stream_data_len_ <= 0) { // input
        *dest_len = 0;
        return Filter::FILTER_NEED_MORE_DATA;
    }

    // Fill in zlib control block
    zlib_stream_.get()->next_in = bit_cast<Bytef*>(next_stream_data_);
    zlib_stream_.get()->avail_in = stream_data_len_;
    zlib_stream_.get()->next_out = bit_cast<Bytef*>(dest_buffer);
    zlib_stream_.get()->avail_out = *dest_len;

    int inflate_code = inflate(zlib_stream_.get(), Z_NO_FLUSH);
    int bytesWritten = *dest_len - zlib_stream_.get()->avail_out;

    Filter::FilterStatus status;

    switch (inflate_code) {
    case Z_STREAM_END: {
        *dest_len = bytesWritten;

        stream_data_len_ = zlib_stream_.get()->avail_in;
        next_stream_data_ = bit_cast<char*>(zlib_stream_.get()->next_in);

        SkipGZipFooter();

        status = Filter::FILTER_DONE;
        break;
    }
    case Z_BUF_ERROR: {
        // According to zlib documentation, when calling inflate with Z_NO_FLUSH,
        // getting Z_BUF_ERROR means no progress is possible. Neither processing
        // more input nor producing more output can be done.
        // Since we have checked both input data and output buffer before calling
        // inflate, this result is unexpected.
        status = Filter::FILTER_ERROR;
        break;
    }
    case Z_OK: {
        // Some progress has been made (more input processed or more output
        // produced).
        *dest_len = bytesWritten;

        // Check whether we have consumed all input data.
        stream_data_len_ = zlib_stream_.get()->avail_in;
        if (stream_data_len_ == 0) {
            next_stream_data_ = NULL;
            status = Filter::FILTER_NEED_MORE_DATA;
        } else {
            next_stream_data_ = bit_cast<char*>(zlib_stream_.get()->next_in);
            status = Filter::FILTER_OK;
        }
        break;
    }
    default: {
        status = Filter::FILTER_ERROR;
        break;
    }
    }

    return status;
}

bool GZipFilter::InsertZlibHeader()
{
    static char dummy_head[2] = { 0x78, 0x1 };

    char dummy_output[4];

    // We only try add additional header once.
    if (zlib_header_added_)
        return false;

    inflateReset(zlib_stream_.get());
    zlib_stream_.get()->next_in = bit_cast<Bytef*>(&dummy_head[0]);
    zlib_stream_.get()->avail_in = sizeof(dummy_head);
    zlib_stream_.get()->next_out = bit_cast<Bytef*>(&dummy_output[0]);
    zlib_stream_.get()->avail_out = sizeof(dummy_output);

    int code = inflate(zlib_stream_.get(), Z_NO_FLUSH);
    zlib_header_added_ = true;

    return (code == Z_OK);
}

void GZipFilter::SkipGZipFooter()
{
    int footer_bytes_expected = kGZipFooterSize - gzip_footer_bytes_;
    if (footer_bytes_expected > 0) {
        int footer_byte_avail = std::min(footer_bytes_expected, stream_data_len_);
        stream_data_len_ -= footer_byte_avail;
        next_stream_data_ += footer_byte_avail;
        gzip_footer_bytes_ += footer_byte_avail;

        if (stream_data_len_ == 0)
            next_stream_data_ = NULL;
    }
}

} // namespace net
